This invention relates to a device for the nondestructive ultrasonic testing of tubular goods for detection of small internal cracks and other types of discontinuities or imperfections. More specifically, the device of the instant invention permits on-site inspection of the drill pipe employed in the drilling operation, or well casing or tubing while it is being set, and is particularly useful since it maintains the ultrasonic search units in fixed and constant position relative to the pipe, and enables inspection of the pipe as it is being tripped into the borehole under the rugged conditions prevailing on the rig floor. The novel apparatus permits ready identification of flawed tubular goods which might produce drilling string failures if used when drilling is recommenced.
The use of ultrasonic testing techniques, and specifically of ultrasonic crystals, for detecting discontinuities in metal products is a common mode of nondestructive testing. The crystals employed are typically piezoelectric crystals made of a material such as quartz. These crystals produce ultrasonic vibrations in response to a voltage of appropriate frequency impressed upon the crystal. When inspecting a tubular product for internal flaws using a reflection method, the crystal is maintained in a position relative to the surface of the product to transmit a short duration sonic wave pulse into the product at an angle such that a defect or discontinuity will cause the waves to be reflected to the crystal and produce a voltage response in the crystal. Since the crystal is de-energized immediately following the pulsed emission of a wave, reflected waves are received during de-energized periods, and hence the reflected waves will produce a discernible signal which may be monitored, for example, on a cathode ray tube or a strip chart recorder. Pulse repetition rates between 60 and 2000 pulses per second are employed in various types of inspections.
Typically, an ultrasonic inspection device will be calibrated using a standard identical to the goods being inspected. The standard may have one or more discontinuities of known magnitude so that the response of the device to known imperfections may be ascertained, and standards for accepting or rejecting the inspected goods may be established.
Ultrasonic inspection techniques are most typically employed at the site of manufacture of the articles being inspected. Thus, plate or tubular goods are typically inspected at the manufacturing plant using techniques which are well known in the art. However, the on-site inspection of tubular goods presents different and unique problems.
In well drilling operations, drill pipe failure can be a costly and time-consuming occurrence. Washouts or drill string breakage can occur frequently if drill pipe with sufficiently serious imperfections is employed. Most frequently such failures result from internal flaws in the tubular goods being used. Contrasted with such a failure, it becomes necessary to trip the pipe out of the borehole to replace the failed joint. In the case of drill string breakage, it is also necessary to fish the parted portion of the string from the borehole before drilling can be recommenced. Hence, the value of an efficacious method of inspection, particularly for internal flaws in drill pipe is obvious.
During drilling operations, the drill string is frequently tripped into and out of the borehole to replace a worn drill bit, to set casing at various levels or conduct other operations. During these trips, it is preferred to stack the drill pipe vertically within the well derrick rather than transporting it from the elevated rig floor to racks maintained at ground level. In offshore drilling operations, it is also common to stack drill pipe vertically. Inspection of a drilling string is desirably conducted periodically, e.g., every two or three months, to detect the existence of flaws on drill pipe which would render the pipe susceptible to failure in subsequent drilling operations. Hence to provide most efficient inspection of tubular goods in well drilling operations, it is necessary to provide an inspection device which can inspect tubular goods in a vertical position in the well derrick. With such a device inspections could be conducted during a tripping operation made necessary by factors such as a replacement of a worn drill bit. Furthermore, since it is necessary to join individual stands of pipe (comprising typically two or three pipe joints or sections) at the rig floor level when assembling a drilling string, it is necessary that a useful inspection device be readily engaged and disengaged from about the pipe being inspected.
The sensitivity of ultrasonic inspections, however, can be adversely affected by the severe conditions prevalent on a drilling rig. A suspended pipe can move laterally or can be vibrating as a result of the insertion or withdrawal operation. Such conditions make it difficult to maintain adequate sonic coupling between the search unit and the pipe. However, such movement can alter the angles at which the sonic emissions enter the wall of the member being inspected. It is accordingly necessary to provide a rugged device to conduct such on-site inspection to obtain the most accurate and dependable readouts.